1. Field of the Invention
The present invention relates to an electronic endoscope, especially to an electronic endoscope that can display a fluorescent image.
2. Description of the Related Art
Currently, an electronic endoscope that enables a so-called fluorescence observation is known. In such an electronic endoscope, the property is utilized that when excitation light is emitted, a normal part of an observation subject generates fluorescent light; on the other hand, a diseased part, such as a cancer part, generates no fluorescent light. In certain such electronic endoscopes, a plurality of imaging optical systems are provided, so that a fluorescent image and a normal image based on reflected light of white light are generated and displayed on a monitor simultaneously.
On the other hand, in a current electronic endoscope that enables a fluorescence observation and that has a single imaging optical system, obtained normal images and fluorescent images are once stored, then processes are carried out on each of them. After carrying out the processes, a normal image and a fluorescent image are displayed on a monitor. The reason for carrying out different processes for a normal image and for a fluorescent image is that the fluorescent light from a body organ based on the excitation light is weaker than the reflected light of the white light, so that image signals based on the fluorescent light should be amplified; on the other hand, amplifying image signals based on the reflected light of the white light may cause halation in a normal image, so a subject may not be observed.
Providing a plurality of imaging optical systems in an electronic endoscope complicates the device, increases the manufacturing cost. On the other hand, in a current electronic endoscope having a single imaging optical system, a normal image and a fluorescent image as real time images of the same subject can not be generated by brightness control, and can not be displayed.